3.1 Introduction

Breast imaging is currently undergoing major changes following the widespread implementation of full-field digital mammography (FFDM) equipment. The advantages of digital mammography over film-screen mammography (FSM) stem from the ability to manipulate the image electronically; brightness or contrast can be adjusted, and the image can be magnified after the digital mammogram is completed. These features make it easier to see subtle differences between tissues.

Mammographic breast density appears to be a major risk factor for interval breast cancer. The ability to increase contrast when imaging dense tissue is very important. Digital mammography is more accurate in women under the age of 50, women with radiographically dense breasts,and premenopausal or perimenopausal women.

Despite recent major advances, mammography remains a very technically demanding imaging procedure. This is partly because the breast is entirely composed of soft tissue, and normal and abnormal tissues have very similar radiographic properties. In addition, the appearance of "normal" breast tissue varies enormously from woman to woman. Asymmetric breast tissue is encountered relatively frequently, having been reported to occur in 3% of screening and diagnostic mammograms. The American College of Radiology (ACR) BI-RADS® defines four different types of asymmetric breast findings: asymmetric breast tissue, densities seen in one projection, architectural distortion, and focal asymmetric densities. These findings are significant because they can indicate a neoplasm, especially if an associated palpable mass is present.